<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>

    .box {
        position: relative;
        width: 400px;
        height: 400px;
        border: 1px solid black;
    }
    .div1 {
        position: absolute;
        height: 200px;
        width: 200px;
        border: 1px solid pink;
        /*transform: translate(-50%,0);*/
        left: 0;
        top: 0;
        right: 0;
        bottom: 0;
        margin: auto;
    }
    a:link{
        color: pink;
        font-size: 20px;
        text-decoration: none;
    }
</style>
<body>
    <div class="box">
        <div class="div1" >
            <a href="#">有链接属性</a>
            <progress></progress>

        </div>
    </div>
    <script>
        if(! "a" in window){
            var a = 1;
        }
        var a = 4399<0||typeof (4399+'')
        //alert(3==true)
    </script>
</body>
</html>